The present invention relates to an improved press cushion and, more specifically to a press cushion cylinder assembly with a vented rod end chamber connected with a source of clean air.
The use of a cylinder assembly as a press cushion is well known. Originally, helical coil springs were used in dies for the purpose intended herein, e.g. restraining the workpiece from movement prior to the die contacting the part fully and assisting in returning the workpiece and the die portions to their original positions. In many instances, cylinder assemblies have replaced the helical springs.
These known press cushion cylinder assemblies are equipped with a means to supply fluid under pressure (air, gas, or hydraulic) to the head end of the cylinder chamber. The opposite or rod end of the cylinder chamber is generally vented to atmosphere. A problem occurs in presses using typical die cushion cylinder assemblies when foreign materials are drawn into the rod end chamber from the environment around the press. For example, fluids termed drawing compounds which are used as a lubricant on the material being processed, may literally flood over the die cylinders. This drawing compound and other particles can be inspirated into the vents on the die cylinders and when drawn in, can cause failure of the seals and other components of the die cylinder assembly.
Various piston and cylinder assemblies utilized in association with presses are disclosed in U.S. Pat. Nos. 3,013,791; 3,157,095; 3,267,677; 3,375,001; and 3,490,757. These known assemblies do not contemplate that clean air from a source of low pressure air or from an environment spaced apart from the press will be supplied to an expanding cylinder chamber during operation of the press. In addition, a piston and cylinder assembly for pumping fluid is disclosed in U.S. Pat. No. 3,019,739.